FIELD BOOK OF MAMMALS 



munk and have a rather close superficial resemblance, there is, 

 nevertheless, quite a distinction between the Western and 

 Eastern Chipmunks. The fine striping and slender, more 

 agile build of a typical Western Chipmunk readily distin- 

 guishes it from the broader striped, heavier bodied Tamias, 

 which in many characters more nearly resembles some of the 

 small western Ground Squirrels {Callo s pernio philus) . 



The Western Chipmunks are a large and much diversified 

 group. In the terminology of the mammalogist, they are said 

 to be very plastic; that is, there seems to be a distinct type of 

 Chipmunk for each change of environment; and one rather 

 widely accepted explanation for this is, that the influences of 

 the environment find the Chipmunk to be an easily moulded 

 organism and have modified its characters. Regardless of 

 whether one believes that animals are directly influenced by 

 environmental forces or not, no mammalogist can deny that 

 there is a close correlation between the color pattern of £w- , 

 tamias and the type of country where it is found. ^ 



In the humid, heavily forested, coastal belt of southern 

 British Columbia, Washington, Oregon, and California, we 

 find the largest and most somber colored of all the Chipmunks, 

 the townsendii group. Here the large size is correlated with 

 an abundant food supply and congenial environment, and the 

 dark color with the humidity of the atmosphere. At the other 

 extreme stands the minimus group, living in the open, sun- 

 flooded, arid plains and deserts and well characterized by 

 small size and pale colors. The difference in the appearance 

 of the members of these two groups fully equals the contrast 

 between their respective environments. The gap between 

 the small, pale Chipmunks and the large, dark Chipmunks is 

 bridged over by many variations in size and color pattern. 

 There is scarcely any pecuhar ecological association in western 

 North America which does not have its own peculiar form of 

 Chipmunk, provided the animal can find food there. This 

 accounts for the great number of known species and subspecies 

 which, however they vary, are yet easily recognized as mem- 

 bers of the genus Eutamias. 



Wherever it is found, the Chipmunk is a bright, alert, active 

 creature moving about during most of the daylight hours and, 

 in most cases, easily observed. In general, the species which 

 live on the open plains are shyest, since they are most liable 



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